Production of carboxylic acids

ABSTRACT

1. THE METHOD OF PREPARING CARBOXYLIC ACIDS WHICH COMPRISES: OXIDIZING 1-OLEFINS WITH NITRIC ACID IN A FIRST STAGE OXIDATION IN THE PRESENCE OF A VANADATE SALT PROMOTER AND AN INITATOR SELECTED FROM NITRITE COMPOUNDS AND NITROGEN DIOXIDE AT A FIRST TEMPERATURE BELOW ABOUT 65* C. FOR AT LEAST ONE HALF HOUR, THEN CONTINUING THE OXIDATION IN A SECOND STAGE OXIDATION AT A TEMPERATURE OF 75*C. UP TO ABOUT 110*C. FOR AT LEAST ONE HALF HOUR, AND ISOLATING CARBOXYLIC ACIDS FROM THE MIXTURE OF REACTION PRODUCTS.

United States Patent O 3,839,377 PRODUCTION OF CARBOXYLIC ACIDS Paul H. Washecheck and Charles M. Starks, Ponca City,

Okla., and Owen Portwood, Jr., Janesville, Wis., assignors to Continental Oil Company, Ponca City, Okla.

Filed Jan. 12, 1971, Ser. No. 105,868 Int. Cl. C07c 51/32, 53/22 U.S. Cl. 260-413 20 Claims ABSTRACT F THE DISCLOSURE l-olefins are oxidized with nitric acid in the presence of a vanadate promoter and a nitrite containing initiator to yield a mixture of carboxylic acids and nitrogen containing compounds, including 1nitro-1olen. The yield of carboxylic acids is improved by carrying out the reaction through a low temperature stage followed by a high temperature stage. Production of nitrogen containing compounds in the product mixture is favored by the addition of a salt to the reaction mixture. To effectively recover carboxylic acids from the product mixture, a base may be used to extract acids from the nitrogen containing compounds, while concurrently converting a substantial portion of the nitrogen containing compounds to l-nitro-loletins. The latter are then recycled to the nitric acid oxidation zone and are oxidized to carboxylic acids. Alternatively, the l-nitro-l-oletins may be hydrogenated to yield primary amines.

BACKGROUND OF THE INVENTION Field of the Invention This invention relates to the production of carboxylic acids using oleinic compounds as starting materials, and to the control of process parameters and steps to improve the yields of the acids, and to improve the selectivity attainable between the carboxylic acids and certain nitrogen containing by-products of the process.

Brief Description of Prior Art It is known that carboxylic acids can be produced by the oxidation of olefins with nitric acid. The procedure yields a mixture of the carboxylic acids and nitrogen containing compounds, and is most frequently carried out at a temperature in excess of about 50 C. Since the nitrogen containing compounds have an adverse effect upon the carboxylic acids when the latter materials are employed in commercial practice, it is desirable to effect an eicient separation and purification of the carboxylic acids. Also efforts are constantly going forward to improve the yield of carboxylic acids realized by the olefin oxidation method, and to improve the selectivity as between the carboxylic acids produced and the various nitrogen containing compounds concurrently yielded. Upgrading of the nitrogen containing by-product compounds is also a desideratum dictating further research efforts.

BRIEF DESCRIPTION OF THE PRESENT INVENTION This invention provides a process and various sub-processes carried out thereunder by which the yield and purity of carboxylic acids produced by the nitric acid oxidation of oletins can be improved. The process, in one of its embodiments, further results in the upgrading of nitrogen containing by-products of the olefin oxidation, and in improved control of the extent to which such by-products are produced in relation to carboxylic acid production.

The method comprises oxidizing l-olens with nitric acid in a rst stage oxidation at a first temperature below about 65 C. for a irst period of time of at least one half hour, then continuing the oxidation at a temperature substantially exceeding the first stage oxidation temperature for a period of at least one half hour, and isolating 3,839,377 Patented Oct. 1, 1974 ICC the carboxylic acids from the mixture of reaction products.

Brietiy described, the preferred process of the present invention comprises oxidizing l-Olenic compounds With nitric acid in the presence of a vanadate salt promoter and a nitrite compound as initiator. The oxidation reaction is carried out in two successive temperature stages, the rst stage being at a temperature which is preferably below about 65 C., and the second stage being at a temperature above about C., and preferably above about C.

The oxidation reaction yields a reaction mixture containing a predominance of straight chain carboxylic acids, with the remainder consisting essentially of a mixture of neutral nitrogen containing compounds, one type of which is l-nitro-l-olein compounds. In instances where market demands or other factors may dictate the desirability of increasing the yield of the l-nitro-l-oletin product, or certain upgraded derivatives thereof, an increase in the yield of l-nitro-l-oletin can be accomplished by adding certain salts to the reaction mixture.

Upon completion of the oxidation reaction, the carboxylic acids can be isolated and purified by any suitable method. Preferably, however, the acids are extracted by contacting the oxidation reaction mixture with a base, which may be either an organic or an inorganic material. When the acids are recovered in this manner, a substantial portion of the nitrogen containing compounds in the mixture are converted to the corresponding 1-nitro1ole lin compounds. The l-nitro-l-olefin compounds remaining after extraction of the acid may then optionally be recirculated to the nitric acid oxidation zone where these compounds are converted by oxidation to carboxylic acids to thereby increase the total yield of carboxylic acids, or, alternatively, the l-nitro-l-oletin compounds can be hydrogenated to the corresponding primary amines and are thus upgarded to a more valuable product.

From the foregoing description of the invention, it Will have become apparent that it is an important object of the present invention to provide an improved process for producing carboxylic acids by the nitric acid oxidation of olens.

In another aspect, an objective of the invention is to provide a process by which straight chain carboxylic acids are produced by the nitric acid oxidation of l-nitro-l-oleiin compounds.

A further object of the invention is to provide a procedure for more effectively isolating carboxylic acids from nitrogen containing compounds produced in admixture with the acids upon oxidation of l-oleiin compounds with nitric acid.

An additional object of the invention is to provide an improved process for oxidizing l-olens to produce nitrogen containing compounds and straight chain carboxylic acids, by which process the selectivity as between the nitrogen containing compounds produced and the carboxylic acids is increased.

Another object of the invention is to provide a process for oxidizing oleiins to yield carboxylic acids in which the yield of acids realized is improved by certain temperature controls imposed in the course of the oxidation reaction.

Additional objects and advantages of the invention will become apparent as the following detailed description of the invention is considered in conjunction with the accompanying drawings which illustrate the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block ow diagram schematically illustrating one embodiment of the process of the invention.

FIG. 2 is a block liow diagram schematically illustrating another embodiment of the invention.

3 DETAILED DESCRIPTION O-F PREFERRED EMBODIMENTS OF THE INVENTION The l-olens used as starting materials in the process of the present invention vary widely in molecular weight, but are, in general, aliphatic olefinic materials. The nitric acid employed in the oxidation of the olefins can vary over a wide range in strength, but is preferably from about 8 molar to about 21 molar. Preferably, the nitric acid has a strength of from about 12 molar to about 20 molar.

One of the important aspects of the present invention is the carrying out of the olefin oxidation reaction in two successive temperature stages utilizing a vanadate salt as a promoter, and a nitrite compound or nitrogen dioxide as an initiator material. The initiating eiect of the latter materials is dependent upon carrying out the reaction in the two temperature stages as hereinafter more fully described, and the vanadate compound also functions less effectively as a promoter unless the reaction is carried out in two temperature stages.

We have determined that when the bi-level temperature procedure is followed, the yield and purity of carboxylic acids produced by the process is increased with respect to that which is realized when the process is carried out, either at a single low temperature level or at a single relatively high temperature level. When operating at high temperature alone, the utilization of sodium nitrite as an initiator appears to provide little aid in increasing the yield of carboxylic acids produced by the reaction. While the nitrite compound improves the yield of acids some when carrying out the reaction at a single low temperature level, the quality of the acids produced is poor.

perature stage. In carrying out the reactions in these runs, a three-necked, round-bottomed flask equipped with a condenser, thermometer, mechanical stirrer and an addition funnel was charged with 500 ml. of 15.4 molar nitric acid and 0.23 gram ammonium vanadate (0.002 mole). In those runs in which sodium nitrite was added as an initiator, this material was added at this point in the run. The oxidation reaction mixture as thus made up was then heated to the specified temperature which was to be used in either the first or single stage used in the run. grams of 1octene was then added drop-wise to the reaction iiask.

In the one-stage oxidation reaction, the reaction mixture was stirred until the speci-fied reaction time (as measured from the beginning of the olefin addition) had elapsed. In the case of the two-stage reaction, the total time period was divided into equal halves. The first half of the specified time, the temperature was maintained at the lower value, and in the second half, the temperature was raised to the higher value. Upon completion of the reaction, the mixture was cooled and the organic products were extracted from the reaction product mixture with pentane. The product mixture was then separated into acidic and nonacid fractions, utilizing base to extract the carboxylic acids. (The advantages of the base extraction are hereinafter described.) The acids were then freed from the base by treatment with a mineral acid. The acid fraction was then analyzed by the addition of an external standard, followed by conversion of the acids to esters and quantitative analysis of the esters by gas chromatography.

The results of these runs are set forth in Table I.

TABLE I Weight percent a Temp., C Reaction N No product yield Weight percent acid distribution Mole percent acid yields me a z M Acids Neutrals C5 Cu Cz Total C5 Ce C1 Total 97. 7 23. 8 2. 0 6. 5 28.4 36. 9 2. 1 6. 2 23. 9 32. 2 82. 8 28.2 1. 3 12.1 54.0 67.4 1. 2 9. 7 38. 5 49. 4 44. 4 62. 5 4. 0 18. 4 20. 5 42. 8 1. 9 7. 9 7. 8 17. 6 80.9 33. 0 1. 6 10. 1 43. 5 55. 2 l. 4 7. 9 30. 3 39. 6 85. 5 12.2 1. 2 17. 4 76.1 94. 7 1. 1 14. 3 56. 2 71. 87. 4 10.0 1. 3 16. 4 74.3 92.0 1. 3 13. 9 56. 0 71. 1 87.4 3.9 1. 3 16. 5 75. 9 93. 7 1. 2 13.9 57. 2 72. 3 76. 7 27. 2 1. 5 15. 9 69. 0 86. 4 1. 2 11. 8 45. 6 58. 6 77. 8 28. 3 0.8 14.6 71. 0 86. 4 0. 7 10.9 47. 6 59. 2 74. 5 21. 5 l. 9 17. 6 78. 7 98.2 1. 6 12. 7 50. 5 64. 8 75. 6 21. 4 2.1 16, 1 78.6 96. 8 1. 8 11. S 51. 2 64. 7 80. 2 11. 7 3. 7 18.4 76. 9 99. 0 3. 2 14. 2 53. 2 70. 6 80. 4 14. 4 2. 3 15. 1 81. 3 98. 7 2. 1 11. 7 56. 3 70. 1 80. 6 10.0 2. 8 13. 7 82. 4 98. 9 2.5 10.6 57.3 70.4 79. 4 2. 2 5. 5 12. 9 82. 4 100. 8 4. 8 9. 9 56. 5 71. 1.

1 Determined as: weight of product equals weight of olefin starting material X 100.

In carrying out the reaction, a typical vanadate salt which may be employed is ammonium vanadate. An amount of from about 0.001 mole to about 0.01 mole may be used effectively for each mole of olefin reacted. For this same amount of olefin, from about 0.01 mole to about 0.4 mole of a nitrite salt, typically sodium nitrite, may be employed as an initiator.

The temperature levels at which the reaction is carried out in two stages are preferably a temperature of from about 0 C. to about 65 for the first or low temperature stage, and from about 65 C. to about 110 C. for the second or high temperature stage. Preferably the high temperature stage is carried out at a temperature exceeding about 75 C. The time over which the reaction is carried out at each temperature level is variable. It is preferred that the overall or total reaction time range from about 1 to about 4 hours.

Example 1 A number of oxidation runs were carried out to evaluate the effect of performing the process in two temperature stages, as contrasted with a single high or low tem- From the data set forth in Table I, it will be perceived that higher oxidation reaction temperatures generally result in Ia greater yield of carboxylic acids. AS the temperature is lowered, the yield of the acid and the purity of the acid fraction decreases markedly below about 65 C. When sodium nitrite or NO2 is added to the reaction mixture, the yield and purity of the carboxylic acids produced at the lower temperatures are improved to some extent. However, the yield and purity of the carboxylic acids were still less than optimum.

In those runs where the oxidatio-n was carried out in two stages, i.e., the first at low temperature and the second at a higher temperature, the yield of carboxylic acids was increased over the one-stage reaction, whether carried out at the low temperature or at the high temperature. In addition to the increase in yield of carboxylic acids realized when carrying out the reaction in two temperature stages, it will be perceived that the beneficial initiator effect of the sodium nitrite is more pronounced in those runs where the reaction is carried out at two temperature levels than in those runs where the reaction is carried out at a single temperature.

The reaction product obtained in the nitric acid oxidation of the olenic compounds includes, in addition to the carboxylic acids, a variety of nitrogen-containing compounds. The nitrogen in these compounds appears in several diferent functional groups. Some of the nitrogencontaining compounds which are frequently present are the corresponding 1nitro2nitrate, the 1,2-dinitro, the l-nitro-Z-alcohol and the l-nitro-l-olefin. The mixture of straight chain carboxylic acids and nitrogen-containing compounds is, as such, of little value, however, since, for commercial use of the acids, a relatively high degree of purity is necessary, and many of the nitrogen-containing compounds are of low grade and little usage in the form in which they appear in the product.

It is thus desirable to provide a method for isolating, in a relatively pure state, the carboxylic acids in the product mixture. A mixture of carboxylic acids and amines may be produced simply by hydrogenating the product mixture. There are, however, several disadvantages to this procedure. First, the mixture of acids and amines would, as such, be of little value, and a method for separation of the acids from the amines would have to be devised. Even upon successfully effecting such separation, the amines would consist of a complex mixture which would include hydroxy amines and diamines, as well as the primary amines.

lWe have determined that if the original product mixture yielded by the nitric acid oxidation is treated with base, two advantageous events occur. The carboxylic acids are extracted from the organic product mixture into the base. A convenient method is thus provided for separating the carboxylic acids from the remainder of the reaction mixture. Moreover, the treatment with base has been found to convert a high percentage, in the range of from about 80 to about 95 weight percent, of the nitrogen-containing compounds to the corresponding l-nitrol-olens. The l-nitro-l-olefins produced in this manner may then be hydrogenated to the corresponding primary amines. It has further been significantly determined that l-nitro-l-olen compounds can themselves be oxidized with nitric acid directly to carboxylic acids. Thus, as an alternative to hydrogenation, the nitrolens may be recycled to the oxidation reactor for reaction with nitric acid to yield additional carboxylic acids as hereinafter explained.

Both inorganic bases and organic bases are useful for the extraction of the acids and conversion of the nitrogencontaining compounds to the corresponding l-nitro-loletins. Triethanolamine is a particularly well suited organic base.

A simplified ow diagram of the process as carried out using sodium hydroxide as the acid extraction base is depicted in FIG. l of the drawing. As here shown, the olen feed stock is charged to the oxidation reactor where it is reacted with nitric acid in the presence of a vanadate salt promoter and a nitrite initiator. The oxidation product is then treated with aqueous sodium hydroxide to extract from the product mixture the sodium salts of the carboxylic acids. Remaining in the raffinate phase following the extraction are the l-nitro-l-olens which have been produced by contact of the nitrogen-containing compounds yielded by the oxidation reaction with the sodium hydroxide base. The l-nitro-l-olen compounds may then be hydrogenated to yield primary amines, or may be recycled to the oxidation reactor where, by oxidation with nitric acid, they are in turn converted to carboxylic acids as more fully hereinafter explained.

The sodium salts of the carboxylic acid which are extracted in the aqueous layer are then treated with a mineral acid, represented by the term HX in the ow diagram, to regenerate the carboxylic acids and form the sodium salt of the mineral acid.

The ratio of the carboxylic acids to the l-nitro-l-olefins produced can be varied over a wide range by variation in reaction conditions, as illustrated by the following example of runs in which the reaction conditions were varied as described. In general, the production of carboxylic acids is favored by relative high nitric acid strengths (up to about 20 molar), and by the use of larger volumes of the acid, as well as by carrying out the reaction at two temperature levels as hereinbefore described.

EXAMPLE 2 Nitric acid of a quantity and concentrationspecified in each run tabulated in Tables II-V was charged to a three-necked, round-bottom tiask equipped with a condenser, mechanical stirrer, thermometer, and addition funnel. 0.002 mole of ammonium vanadate was added to the ask. In those runs where the reaction was carried out in two temperature stages as hereinbefore described, sodium nitrite initiator was added in an amount of 0.1 mole. The reaction mixture was then heated to the speciiied reaction temperature. 35 grams of l-octene were then added in a drop-wise fashion. The reaction was terminated after the specified times as set forth in the tables hereinafter, as such time was measured from the start of the addition of the olefin. In the two-stage oxidations carried out at two temperature levels, the reaction period was divided into two equal portions. The rst portion was carried out at temperature T1 and the second portion at temperature T2. The reaction products were isolated by extraction of the reaction mixture with pentane. The carboxylic acids were then isolated by extraction of the pentane solution with sodium hydroxide. lnitro-l-octene was then isolated from the remaining pentane solution, and the weight percent of acids and of l-nitro-l-octene were then determined by analyses. The results obtained in these runs are set forth in Tables II-V.

TABLE II.-EFFECT OF NITRIC ACID CONCENTRATION Weight percent Reaeyield of products HNO3 Temp., C. tion tim Nitro- Run M M1. T1 T2 (hrs Acids oleu 1 15.4 500 1 73. 4 25.8 2 14 500 1 73. 2 28. 6 3 12 500 1 70. 9 34. 6 10 500 1 62. 0 45. 6 15. 4 500 2 80. 6 10. 0 14 500 2 84. 2 7. 7 12 500 2 84. 4 15. 0 10 500 2 70.4 33. 0 8 500 2 65. 5 41. 3 15. 4 500 4 79. 4 2. 2 14 500 4 82. 8 2. 1 12 500 4 85. 7 5. 3 l0 500 4 80. 5 17. 8 15. 4 500 4 80.2 11. 7 14 500 4 82. 4 15. 9 12 500 4 77. 2 23. l 21. 2 500 1 62. 0 9. 0 15. 4 500 1 69. 5 35. 2 14 500 l 66. 6 40.8 21. 2 500 2 61. 3 7. 5 15.4 500 2 74. 5 21. 5 14 500 2 69. 1 34. 1 15.4 500 4 87. 4 3. 9 14 500 4 89. 5 6. 7 12 500 4 84.9 15. 4 15. 4 500 2 85. 5 3. 7 14 500 2 89. 4 4. 7 12 500 2 86.3 11. 0

TABLE IIL-EFFECT OF NITRIC ACID VOLUME Weight percent Reacyield of products M Ml. T1 Tg (hrs Acids olefin 14 500 1 73. 2 28. 6 14 200 1 68. 2 39. 8 14 100 1 59. 3 52. 1 l5. 4 500 4 80. 2 11. 7 15.4 300 4 81. l 16. 6 15.4 200 4 76. 6 26. 0 15.4 4 63. 6 49. 2 l5. 4 500 1 69. 4 38. 7 15. 4 100 1 58. 9 49. 5 14 500 4 89. 5 6. 7 14 250 4 83.6 16. 5

TABLE IV.-EFFECT OF REACTION TEMPERATU RE Weight percent Reacyield oi products Run M Ml. (hrs.) Acids olefin TABLE V.-EFFECT OF REACTION TIME Weight percent Reacyield of products HNO@ Temp., C. tion tim Nitro- M Ml. T1 T2 (hrs Acids olefin EXAMPLE 3 Other olefins besides l-octene were oxidized with nitric acid in the manner described in Example 2. The l-nitrol-olefin products obtained were separated from the carboxylic acids and the weight percent of each determined.

The results of these runs are set forth in Table VI.

TABLE VI.-NITRIC ACID OXIDATION OF OLEFINS Where the 1-nitro-1-olefins are to be converted to amines by hydrogenation, as shown in the flow diagram of FIG. 1, it is desirable to exercise care to prevent significant side reactions, such as the formation of secondary and tertiary amines. In order to accomplish this, the hydrogenation of the nitro-olefins is preferably carried out in two steps as exemplified by the following example.

EXAMPLE 4 2 grams of l-nitro-l-octene were charged to a 100 ml. stainless steel autoclave, along with 10 ml. of absolute methanol and 0.2 gram of 5 Weight percent paladium catalyst. The autoclave was fiushed with three volumes of hydrogen and pressured to about 200 p.s.i. Stirring was then commenced. After about 15 minutes, one equivalent of hydrogen had been adsorbed and the stirring was terminated at the 1-nitro-octane stage of the reduction (that is, saturation of the olefinic double bond).

The remaining hydrogen was then removed, and the reactor pressured to 100 p.s.i. with ammonia, followed by pressurization with hydrogen to a total of 300 p.s.i. After suicient hydrogen had been adsorbed, the catalyst was removed by filtration and the solvent was removed by distillation to give 1.34 grams of l-octylamine. This was a yield of percent. The primary amine was still contaminated with a small amount of tertiary and secondary amines, but not nearly in the quantities formed when the second stage of the hydrogenation utilizing ammonia is omitted from the reaction.

In some instances, it may be desirable to obtain the maximum yield of carboxylic acid at the expense of the quantity of l-nitro olefin compounds produced. We have surprisingly determined that after the nitrogen-containing compounds produced in the nitric acid oxidation reaction have been converted to 1-nitro-1-oleiin compounds by contact of the reaction product with base, the l-nitro-lolefins can themselves be readily oxidized with nitric acid to yield carboxylic acids. This is particularly surprising since the nitro group is generally considered to be strongly deactivating, and it would be supposed that the l-nitro-l-olens would be highly resistant to oxidation. The 1nitro1olefin compounds have, however, been determined to be susceptible to oxidation under substantially the same reaction conditions as the 1-olefins to yield carboxylic acids. Thus, as indicated by the dashed line in the flow diagram schematically portrayed in FIG. 1, the l-nitro-l-olefin compounds produced by contacting the oxidation reaction product with base may be recycled to the oxidation reactor. They are there oxidized with nitric acid in the presence of a vanadate salt promoter (and, if desired, a nitrite-containing initiator) to convert these compounds to carboxylic acids in the same general molecular weight range as the carboxylic acids obtained in the initial oxidation reaction of the l-olefin feed stock.

EXAMPLE 5 A three-necked, round-bottomed flask equipped with a condenser, thermometer, mechanical stirrer and addition funnel was charged with 500 ml. of 15.4 molar nitric acid. 0.004 mole of ammonium vanadate and 0.20 mole of sodium nitrite were added to the acid in the flask. The solution was then heated to 35 C. 35 grams of l-nitro-loctene which was approximately percent pure were added dropwise to the reaction mixture. One hour after the start of the addition of the nitro-olefin, the reaction 'temperature was raised to 95 C. Two hours after the Carboxylic Acid Weight Percent Pentanoic (C) 0.0 Hexanoic (C6) 22.5 Heptanoic (C7) 73.1 Octanoic (C8) 0.0

Total 95.6

The described method of increasing the yield of carboxylic acids produced in the nitric acid oxidation of olens is particularly significant since, even though the nitrogen-containing compounds produced upon such oxidation appear to be intermediates in the production of carboxylic acids, We have determined that merely carrying out the nitric acid oxidation reaction for a longer period of time does not increase the yield of carboxylic acids. Increasing the total reaction time appears to destroy the carboxylic acids produced by the reaction more rapidly than they are further yielded from the intermediate nitrogen-containing compounds, whereas chemical analyses of the carboxylic acids produced by the oxidation of the nitro-olefin indicate that these acids are comparable to those which are produced directly from the olen. This is shown by the data set forth in Table VII, in which the results obtained in carrying out two runs under identical conditions to those set forth in Example 5 are tabulated to allow comparison of results obtained when l-octene was the starting material used in one of the runs, and 1nitro1octene was the starting material used in the other of the two runs.

In the chemical technology, the usual procedure followed for recovering a carboxylic acid from its amine salt is to neutralize the amine salt with a mineral acid, similar to the procedure hereinbefore described as employed when an inorganic base is used for extraction of the carboxylic acids. Since the mineral acid is a stronger acid than the carboxylic acid, the latter is displaced from the amine salt and may be recovered. Again, however, the mineral acid is consumed in the process. We have now surprisingly found that a portion of the carboxylic acids entering into the formation of amine salts can be distilled from an aqueous solution of the amine salts as free carboxylic acids. This development permits the free carboxylic acids to be recovered in relatively pure form from a mixture of oxidation reaction product compounds with no consumption of mineral acid or inorganic base.

A schematic flow diagram illustrative of the process where an amine base is utilized for extracting the carboxylic acids as amine salts thereof is depicted in FIG. 2 of the drawings. As in the case of the ow diagram illustrated in FIG. 1, the olefin feed stock is fed to the oxidation reactor, and the reaction product, consisting essentially of carboxylic acids and nitrogen-containing compounds, is then contacted with an aqueous solution of a suitable amine, such as triethanolamine. The product mixture to which the amine solution has been added then separates in two phases. 'Ihe aqueous phase contains a solution of amine salts of the carboxylic acids yielded by the nitric acid oxidation, and also any excess of the amine not consumed in the neutralization. The other phase which separates contains the 1nitro olefin compounds which are base contacted derivatives of the nitrogen-containing compounds produced by the nitric acid oxidation reaction. As shown in the flow diagram, the 1- nitro olefin compounds may be recycled to the oxidation reactor as hereinbefore described to produce additional carboxylic acids, or may be hydrogenated to yield more valuable primary amine products.

The aqueous phase containing the amine salt may then be steam distilled in accordance with the present invention to yield a distillate which consists of a mixture of water and free carboxylic acids. The still residue or bottoms remaining after such distillation consists of a mixture of amine salts not decomposed during the distillation A problem which renders the process of recovery by inorganic base of the carboxylic acids from the nitric acid oxidation product less than optimum economically is the irreversible consumption of the inorganic base employed (which is converted to a stable salt), and of the mineral acid used for neutralizing the base solution following extraction to free the carboxylic acids. This irreversible consumption of raw materials adds to the cost of the carboxylic acid product. As an alternative, and in some instances, preferred, procedure, organic bases, and specifically amines, may be used for the isolation of the carboxylic acids. It is known that carboxylic acids form water soluble salts with such amines. Thus, the carboxylic acids 4which are formed upon oxidation of olenic materials with nitric acid in the manner described can be extracted from mixtures of these compounds with nitrogen-containing compounds by treatment of the reaction product with amines. Extraction by formation of water soluble salts with amines is also useful for increasing the yield of carboxylic acids, since the l-nitro-lolefins formed upon Contact with the base can be recycled to the nitric acid oxidation zone to produce additional extractable carboxylic acids.

and the basic amine freed from a portion of the salt as a result of the distillation. This mixture (the still bottoms) can be recontacted with more of the nitric acid oxidation product containing carboxylic acids and nitrogen-containing compounds to extract more of the carboxylic acids, and convert more of the nitrogen-containing compounds to the l-nitro olefin derivatives. Thus, even though only a portion of the carboxylic acid is freed from the amine salt during the distillation, and equivalent quantity of amine base is also freed concurrently. This free amine can be used to extract more acid, and thus the process is much more eicient as a continuous process than as a batch process.

In lieu of the use of an organic amine base having a normal boiling range for the purpose of extracting the carboxylic acids from the nitric acid oxidation reaction product, a volatile amine may be employed for this extraction. After the extraction of the acid from the mixture, the volatile amine is distilled from the aqueous solution of its carboxylic acid salts to recover the free amine. In this case, the residue or bottoms remaining after distillation is a mixture of free acid and amine salt. The free amine distilled over is recirculated to the prod- 11 uct extraction point, and used to extract more of the carboxylic acids from the nitrogen-containing compounds. The free acid is separated from the aqueous amine salt solution, and this latter solution then returned to the distillation location.

In summary, then, by the use of organic amines for the purpose of providing the base for extraction of carboxylic acids from the mixture of compounds produced in the nitric acid oxidation of oleiins, either a portion of the carboxylic acids may then be freed from the amine salts and distilled over, or a portion of amine base may be freed from the salts in solution and can be distilled -from the aqueous solution to leave free carboxylic acid.

Which type of distillation occurs will depend upon the particular type of amine which is used as the base for the extraction.

Example 6 25 grams of octanoic acid were dissolved in 500 ml. of pentane. This solution was shaken in a separatory funnel with an equivalent molar quantity of triethanolamine dissolved in 1 liter of water. The mixture was allowed to separate into two phases. The organic phase was dried and the pentane was removed. A small quantity of octanoic acid which was not converted to salt and extracted remained. The aqueous phase was subjected to steam distillation. The distillate consisted of a two phase mixture of Water and octanoic acid in the amount of 16 grams.

In some instances, it is preferable to favor the production of the nitrogen-containing compounds produced by the nitric acid oxidation, as compared to the quantity of carboxylic acids yielded. Such is the case, for example, where the market for the primary amine compounds derived from the nitrogen-containing compounds produced by the nitric acid oxidation is more attractive than the current market demand for carboxylic acids. We have determined that by adding to the nitric acid oxidation reaction mixture carried out at relatively high temperatures, certain anions in the form of their salts, the nitrogencontaining compounds may be made to predominate in the reaction product. The increase is largely due to production of increased quantities of nitronitrate compounds. Although the function of the added salts is not fully understood, it is hypothesized that a salt eiect occurs which saturates the acid layer, and prevents the initially formed product from being further oxidized to additional carboxylic acids. As has been hereinbefore demonstrated, the nitrogen-containing compounds produced in the nitric acid oxidation reaction are converted to l-nitro-l-olein when the reaction mixture is treated with base. It has also been shown that the l-nitro-l-olens can be further oxidized with nitric acid to yield additional carboxylic acids if desired, or may be hydrogenated to yield -valuable primary amines. In salting the nitric acid reaction mixture, sulfate salts are preferably utilized for the purpose of selectively controlling the reaction to favor the production of the nitrogen-containing compounds. Other salts may also be utilized, however, including bromide, chloride, lluoride and nitrate salts.

Example 7 38 grams of sodium sulfate and 100 ml. of 15.4 molar nitric acid were charged to a 500 ml. three-necked ask tted with a stirrer, condenser, thermometer and dropping funnel. After the reaction mixture had been heated to 80 C., l-octene was added over a half hour period while maintaining the temperature at 80 C., with a water bath. The resulting mixture was then diluted with 200 m1. water and extracted three times with pentane. The pentane extracts were in turn washed four times with 1 molar sodium hydroxide to form the l-nitro-l-olein and to remove the carboxylic acids. After drying, the concentrated pentane extracts gave 25 grams of l-nitro-l-octene which amounted to a yield of 71 percent. When the reaction is carried out at temperatures below C. in a single step, l-octene is the major product recovered, with only a small amount of the desired l-nitro-l-octene being formed.

Example 8 The run carried out in Example 7 was repeated using 10 grams of ammonium sulfate. Again, the predominant product was 1nitro1octene.

Although certain preferred embodiments of the invention have been herein described, it will be understood that various changes and innovations can be eiected in the described procedure, and in the materials employed, without departure from the basic principles of the invention. The process proposed can be used in whole or in part, and the alternative steps which are described may be more feasible and valuable in some instances than in others. Variations and changes in the described procedure which continue to rely upon the basic principles underlying the invention, however, are intended to be circumscribed by the spirit and scope of the invention except as the same may be necessarily limited by the appended claims or reasonable equivalents thereof.

What is claimed-is: 1. The method of preparing carboxylic acids which comprlses:

oxidizing l-olens with nitric acid in a rst stage oxidation in the presence of a vanadate salt promoter and an initiator selected from nitrite compounds and nitrogen dioxide at a first temperature below about 65 C. for at least one half hour; then continuing the oxidation in a second stage oxidation at a temperature of 75 C. up to about 110 C. for at least one half hour; and

isolating carboxylic acids from the mixture of reaction products. 2. The method defined in claim 1 wherein the nitric acid utilized in said oxidation reaction has a strength of from about 8 molar to about 21 molar.

3. The method defined in claim 1 and further characterized to include the step of adding to the oxidation reaction mixture, a salt selected from the group consisting of sulfate, chloride, bromide, lluoride and nitrate salts whereby the amount of nitrogen-containing compounds in the mixture of reaction products is increased.

4. The method dened in claim 3 and further characterized as including the additional steps of:

contacting said nitrogen-containing compounds with a base to convert a substantial portion of said nitrogencontaining compounds to 1-nitro-1-olefins; then oxidizing said l-nitro-l-olens with nitric acid in the presence of a vanadate salt at a temperature of from about 0 C. to about 110 C. to yield carboxylic acids.

5. The method defined in claim 3 and further characterized as including the additional steps of contacting said nitrogen compounds with a base to convert a substantial portion of said nitrogen compounds to l-nitro-l-olefins; then hydrogenating said 1-nitro-l-oletin compounds to yield primary amines.

6. The method dened in claim 1 wherein isolation of carboxylic acids from the mixture of reaction products is accomplished by extracting organic products in an organic solvent;

treating the organic solvent solution of extracted organic products with an aqueous base solution to form a two phase system including an aqueous phase solution of salts of said carboxylic acids; and

freeing the carboxylic acids from their salts.

7. The method defined in claim 6 wherein said base solution is a solution of an amine, and said carboxylic acids are freed by distilling the aqueous solution of amine salts of said carboxylic acids.

8. The method defined in claim 7, further characterized in that the amine selected is such that upon distillation of the aqueous solution of amine salts a mixture of free carboxylic acids and water are recovered overhead, and including the step of recycling the bottoms from said distillation for use in treating the organic solvent solution of extracted organic products.

9. The method defined in claim 8 wherein said amine is triethanolamine.

10. The method defined in claim 6 wherein said base solution is a solution of a volatile amine, and said carboxylic acids are freed by distilling the aqueous solution of amine salts of said carboxylic acids to convert a portion of the amine salts to free amine removed as overhead in the distillation, and free carboxylic acids remaining as bottoms during the distillation.

11. The method defined in claim 6 wherein said base solution is a solution of an inorganic base, and wherein the carboxylic acids are freed from their salts by treating the salts with a mineral acid.

12. The method dened in claim 6 wherein the aqueous solution of salts of said carboxylic acids is separated from an organic phase of said two phase system;

and wherein said organic phase is then subjected to hydrogenation to yield a reaction product containing primary amine compounds.

13. The method defined in claim 12 wherein said hydrogenation is carried out in two sequential steps comprising:

contacting said organic phase with hydrogen under a pressure of about 200 p.s.i. in the presence of a hydrogenation catalyst for a time effective to saturate double bonds in olefinic compounds contained in said organic phase; then contacting said organic phase with hydrogen in the presence of a hydrogenation catalyst at a pressure and for a time effective to convert compounds containing nitro groups to amines.

14. The method defined in claim 6 wherein the base is an inorganic base.

15. The method defined in claim 6 wherein the base is triethanolamine.

16. The method defined in claim 6, further characterized in that the two phase system includes a nonaqueous phase of nitrogen-containing compounds which are predominantly l-nitro-l-olefins, and including the step of recycling said l-nitro-l-olefins back to said oxidation reaction.

17. The method defined in claim 6, further characterized-in that the two phase system includes a nonaqueous phase of nitrogen-containing compounds which are predominantly 1-nitro1olens, andA including the step of hydrogenating said l-nitro-l-olefins.

18. The method of producing .carboxylic acids which comprises oxidizing l-nitro-l-oleliii compounds with nitric acid having a strength of from about 8 molar to about 21 molar in the presence of an initiator selected from nitrite compounds and nitrogen dioxide in a first stage oxidation at alfirst temperature below about C. for at least one half h our followed by a second stage oxidation at a second temperature of C. up to about 110 C. for at least one half hour.

19.' The method defined in claim 18 wherein the nitric acid strength is from about 12 molar to about 20 molar.

20.V The method defined in claim'18 wherein a vanadate salt'promoter is employed and the initiator is a nitrite compound.

References Cited UNITED STATES PATENTS 2,347,453 3/1953 Gardner et a1. 26o-533 R 2,347,464 3/1953 R6b6rts6ne;a1.- 26o-533R 3,692,330 9/1972 charamei et a1. 26o- 533 R 2,995,523 3/1961 Bowden et ai. 26o-533 R 3,549,696 12/1970 Duroux et a1. 26o- 533 R 3,433,330 3/1969 Wilkes 26o-54o x 3,536,704 6/1971 Buis 26o-540 x FOREIGN PATENTS 163,674 3/1965 U.s.s.R. 26o- 54o OTHER REFERENCES Noller, Chem. Org. Cmpds. (1965), pp. -182.

40 LORRAINE A. WEINBERGER, Primary Examiner R. D. KELLY, Assistant Examiner U.S. Cl. X.R. 

1. THE METHOD OF PREPARING CARBOXYLIC ACIDS WHICH COMPRISES: OXIDIZING 1-OLEFINS WITH NITRIC ACID IN A FIRST STAGE OXIDATION IN THE PRESENCE OF A VANADATE SALT PROMOTER AND AN INITATOR SELECTED FROM NITRITE COMPOUNDS AND NITROGEN DIOXIDE AT A FIRST TEMPERATURE BELOW ABOUT 65* C. FOR AT LEAST ONE HALF HOUR, THEN CONTINUING THE OXIDATION IN A SECOND STAGE OXIDATION AT A TEMPERATURE OF 75*C. UP TO ABOUT 110*C. FOR AT LEAST ONE HALF HOUR, AND ISOLATING CARBOXYLIC ACIDS FROM THE MIXTURE OF REACTION PRODUCTS. 